The dehydrogenation of dehydrogenatable hydrocarbons to produce unsaturated hydrocarbons is well known in the art. The typical process involves contacting the dehydrogenatable hydrocarbon with a dehydrogenation catalyst under dehydrogenation conditions to produce a mixture of dehydrogenated compounds and unconverted hydrocarbons. Usually the dehydrogenation is carried out in the presence of steam with the liberation of hydrogen. It is also known that dehydrogenation, for example ethylbenzene to styrene, is endothermic in nature and thus the temperature of the catalyst bed decreases significantly during the progress of the reaction, thus lowering the conversion of ethylbenzene to styrene. The limitation of conversion arises from the fact that the equilibrium conversion of ethylbenzene is lowered and the rate of ethylbenzene dehydrogenation decreases as the reaction temperature decreases. The decrease of temperature adversely affects not only the conversion level but also the selectivity for styrene since at equilibrium conditions only undesirable side reactions continue to take place. One method found in the art for maintaining the reaction temperature is to introduce oxygen or an oxygen containing gas which will burn the hydrogen formed during the dehydrogenation reaction thus increasing the temperature of the effluent stream and consequently increasing the conversion of the ethylbenzene to styrene.
The combustion or oxidation of hydrogen with oxygen takes place in the presence of an oxidation catalyst. A number of oxidation catalysts are known in the art. For example in U.S. Pat. No. 4,914,249 an oxidation catalyst is described which comprises a solid porous support such as alumina which has been impregnated with a Group VIII noble metal such as platinum, a Group IVA metal such as tin followed by calcining of the impregnated support and finally impregnating the calcined support with a compound containing lithium followed by a final calcination. The patentees claim that such a catalyst has superior stability and performance than previous catalysts. In U.S. Pat. No. 4,565,898 an oxidation catalyst is described which comprises a Group VIII noble metal, a Group IVA metal and a Group I or II metal dispersed on an alumina support which has been calcined at a temperature in the range from about 900° C. to about 1500° C.
In contrast to this art applicants have developed a catalyst for the selective oxidation of hydrogen in a dehydrogenation process which uses a lithium aluminate as the support for the catalytic metals. Additionally, applicants' catalyst is a layered catalyst comprising an inert inner core such as cordierite and an outer layer of a lithium aluminate bonded to the inner core and having the catalytic metals, e.g., platinum and tin dispersed only on the outer layer.
Layered catalysts are also known in the art as for example in U.S. Pat. No. 6,177,381 which discloses a layered catalyst having an inert inner core and an outer layer where the outer layer can be a refractory inorganic oxide and can optionally contain an alkaline metal. However, there is no mention in the '381 patent of having a layer composed of lithium aluminate.